Are you for growth or austerity? Do you sympathise with the Greeks, or regard them as getting what they deserve? If you disagree with something you read, do you ever change your mind, or do you shout rubbish and chuck it in the bin? Since the days of Socrates, civilisation has honed the art of reason to resolve conflict and deliver harmony. Yet people of like background and education can disagree about everything. Why?

I sometimes wonder that I write for the Guardian when what I say seems to anger so many readers. Most people buy a newspaper not to be prised from their settled opinion but to find it confirmed and comforted. They would not be dragged from it by wild horses, let alone the old nag of reason. A newspaper is their tribal notice board, their badge, their identity.

Nor is that all. Tribes of left and right tend to buy the shop. They take their politics table d'hôte, not à la carte. Those on the left are for more public spending, higher taxes, no war and a tolerance of scroungers, those on the right the exact reverse. Once they have opted for Labour or Conservative (or the obscure freemasonry of liberal democracy), they surrender their political virginity to the party line, lie back and enjoy it – usually for life.

I have a problem with this. I opposed the Iraq and Afghan wars, would abolish Trident, end prison for nonviolent offenders and legalise drugs. But I support the government on NHS reform, students fees and targeting social benefits. I am a UN-enthusiast, but an aid sceptic. Gays should enjoy full civil rights but I find ethnic minorities over-cosseted. All this I regard as a coherent political outlook.

Not many others do. Friends and acquaintances find my portfolio of views either mischievous or mad, and mutter darkly about my probable need of treatment. Dear Abby, are they right?

At last we have some help. It is from the American political scientist, Jonathan Haidt, and his fascinating voyage of discovery through the social psychology of politics, The Righteous Mind. Haidt, a lifelong liberal, was baffled at why so many poor and working-class voters kept supporting conservative politicians when it was clearly against their interest.

Haidt's answer is not just that politics is seldom purely about money. Conservatives are also more in touch with what he calls the "taste buds" of politics. They understand human intuition. They score on such emotions as loyalty to the nation or group, desire for security and authority and a concern for religious and moral purity. Liberals cover just two bases, a sense of fairness and compassion for strangers, thus missing out on a large chunk of human intuition and concern. Above all, they rely too much on an appeal to reason.

To Haidt, reason is not how people wrestle with a problem to find a path to the right answer. That was for the Greeks (the ancient ones). Reason is rather a weapon we deploy to persuade others that we are right, and they use to prove us wrong. It is not a coming together but a driving apart. As David Hume observed, reason is subordinate to the passions. It rides into battle on the elephant of intuition. Hence the advice of modern political tacticians, that politicians should always "talk to the elephant first". Conservatives are good at talking to elephants.

So what determines these dominant intuitions, that they are so resistant to reason? Psychologists now believe that we owe our political views not to any argued programme, but to some gene pool or acquired tribal loyalty, parental, territorial, educational or occupational. It is part nature, part nurture. Loyalty to a profession can be as fanatical as to a family: most lawyers, doctors, soldiers and scientists in my experience believe their profession can do no wrong (unlike, of course, journalists).

This may seem a mere updating of WS Gilbert's cry that "every boy and every gal" is delivered into the world "either a little liberal or a little conservative". But what to Gilbert may have seemed a random attractor of Victorian politics is, in modern America, leading to an increasingly furious polarisation. To many foreigners, America seems a land divided between hysterias, driven apart by round-the-clock news and opinion, in which information inflames rather than calms preconceived opinion.

Studies suggest these political divergences may lie far deeper than we think, in our neurological pathways. Even in mild-mannered Britain, such cross-border adventures as red Tories and blue Labour gain little traction. Opinions reflect insecurity and fear of the unknown: as when America lurched to the patriotic and illiberal right after 9/11. In some American cities, the sociologist Bill Bishop has noted (in The Big Sort) that polarisation is producing a "political ethnic cleansing" as people find they cannot live near others of different views. If political attitudes are becoming that neurotic, it is doubly tragic that people live apart. A cartoon shows a divorcing father explaining to his child, "It is because I want what is best for the country and your mother doesn't."

Yet Haidt offers me only limited help. Whatever intuition he thinks holds me in thrall remains a mystery to me. I believe – as do most people – that I approach any political issue with an open mind, driving towards it in the chariot of reason. I think I can see tribal bigotry at a hundred paces and can fell it with a Socratic blow. I can only assume that Haidt is roaring with laughter, that somewhere in his political anthropology he will unearth a tribe that laced my mother's milk with scepticism and programmed me to a contrarian view of life.

These debates always turn into pleas for liberal tolerance, for a respect for other people's opinions, drawing strength from Stephen Pinker's thesis that, whatever else is amiss, the world is becoming a less violent place. But tolerance is itself a privilege of security. Intellectually it is appeasement. I do not want to tolerate those who disagree with me, I want to persuade them they are wrong. Haidt may cry, "Why can't we all just get along?" The answer is we can't. The best we can do is not murder each other in the process.